Meghan Hodges
Soil pollution is a pressing issue, with far-reaching consequences for the environment and human health. The growing industrialisation of the world has led to a significant amount of soil degradation, with human activities such as intensive agriculture, increasing urbanisation, and industrial activities being largely to blame. Soil remediation is the practice of cleaning up contaminated land to reduce the concentration of pollutants and prevent their spread. Various techniques can be employed to remediate polluted soil, including physical methods such as soil washing, and biological treatments such as bioremediation, which uses microorganisms to break down contaminants. Other methods include chemical oxidation, stabilisation, and thermal desorption. Preventative measures are also key, with proper waste management and the reduction of chemical pesticides and fertilisers being vital to curb soil pollution.
| Characteristics | Values |
|---|---|
| Cause | Human activities such as industrial accidents, intensive agriculture, increasing urbanization, and poor waste disposal methods |
| Impact | Land degradation, soil erosion, salinization, compaction, acidification, and contamination with heavy metals, hydrocarbons, and other pollutants |
| Prevention | Proper waste management, minimizing the use of chemical pesticides and fertilizers, and adopting pollution prevention strategies |
| Treatment Techniques | Soil washing, bioremediation, chemical oxidation, soil stabilization, thermal desorption, steam-enhanced extraction, air injection, and vacuum extraction |
| Resources | FAO's Environmental Management Toolkit, GSP's Online Database on Best Management and Remediation Techniques for Polluted Soils, and State of Knowledge of Soil Biodiversity |
| Professional Services | Soil remediation services, environmental firms, and companies specializing in waste collection and treatment |
| Natural Techniques | Phytoremediation (using plants and trees to absorb pollutants), using fungi to break down pollutants, and composting for organic substances |
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What You'll Learn
Using plants, trees, fungi and bacteria
Using plants, trees, fungi, and bacteria to recover polluted soil
Plants absorb and use nutrients from the soil, including toxins, providing a natural way to clean contaminated land. Some plants can absorb certain toxins and can be placed in areas of contamination. For example, sunflowers have been used to absorb radiation on the site of the Chernobyl nuclear disaster, while mustard greens can absorb lead and have been used on playgrounds in Boston. Willow trees are excellent absorbers and store heavy metals in their roots, while poplars absorb a lot of water and can take in hydrocarbons from petrochemical pollution.
Trees can also play a significant role in waste cleanup by absorbing toxins from the soil and nearby water sources. The larger and faster-growing a tree is, the more effectively it can remove pollutants. Phytoremediation is a process that uses green plants, including trees, to remove, degrade, or stabilize pollutants and contaminants, such as toxic metals, from soil or groundwater. This method has been used for many decades as a low-cost alternative to other cleanup methods.
Fungi, such as mushrooms, have the unique ability to break down chemical pollutants, including oil and pesticides, and extract or bind heavy metals, even radiation. Mycoremediation is a method that utilizes the fungi mycelium (the vegetative part of a fungus) to remediate contaminated soil sites. The enzymes produced by mushrooms are efficient in breaking down various pollutants, harnessing fungi's natural decomposition capabilities to restore and regenerate land.
Additionally, microbial bioremediation employs microorganisms to reduce the toxicity of pollutants, especially organic contaminants. These microbes can break down and metabolize contaminants by using them as a food source. This method has been well-studied and has the potential to effectively recover polluted soils.
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Soil washing with liquid
Soil washing is a common remediation technique used to remove organic contaminants from soil. It involves using washing agents such as water, saponin, organic acids, chelating agents, surfactants, and low-molecular-weight organic acids to extract pollutants from the soil and react them to form insoluble compounds. This process is particularly effective for removing heavy metals and decreasing environmental risks in polluted areas.
When using liquids for soil washing, it is essential to consider the type of agent, concentration, pH, contact time, and the solid-liquid relationship. For example, Gao et al. used the precipitation method by adding NaOH to a spent saponin solution to remove heavy metals. The recovery efficiencies of Pb, Ni, and Cr were highest at a pH of 10.9. Mukhopadhyay et al. used FeCl3 to precipitate As from a spent soapnut saponin solution, achieving up to 87% removal at a low dosage and pH 8.
In the case of more complex or toxic contaminants, such as PHs, PAHs, and PCBs, advanced oxidation processes (AOP) can be applied to form OH radicals and selectively degrade the target contaminants. This approach not only eliminates the contaminants but also recovers the extraction agents for reuse. Anodic oxidation processes have been highlighted as an effective method for treating chlorinated agents.
Soil washing is typically performed ex situ, using extracting reagents to remove hazardous metals from the soil into an aqueous solution. However, wastewater generated during this process can pollute surrounding environments, including agricultural fields and groundwater. In situ soil washing, or "soil flushing," may be preferred in certain contexts, such as in paddy fields with an impervious hardpan that hinders vertical water movement.
Overall, soil washing with liquids is a versatile and effective method for remediating polluted soils, offering high removal efficiencies for various contaminants, including heavy metals and organic compounds. By selecting appropriate washing agents and optimizing conditions, safe and environmentally friendly soil remediation can be achieved.
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Steam-enhanced extraction
A typical SEE system consists of a steam generator, a thermal well field, extraction wells, pumps, and an effluent treatment system. The design of the injection and extraction wells, as well as their locations, is critical for optimal results. The injection wells are used to inject steam into the soil, while the extraction wells remove the contaminated groundwater and vapour for treatment. The wells are typically spaced between 15 to 100 ft apart, with deeper sites using wider well spacing.
The steam injection pressure can be regulated through valves on each injection well, with a safe pressure of 0.5 psig (pounds per square inch gage) per foot of overburden above the screen recommended. Pressure cycling can be induced after steam has reached the extraction wells, varying steam injection pressures and rates to create pressure variations and temporal boiling events in the subsurface. This enhances the volatilization of contaminants outside the steam zone, reducing contaminant concentrations.
SEE is particularly effective for treating volatiles such as trichloroethene (TCE), tetrachloroethene (PCE), oils, and light non-aqueous phase liquids (LNAPLs). It can also be combined with other thermal methods for treating areas with clay layers, as well as less aggressive treatments for source and plume restoration. The technology is well-suited for sites with moderate to high permeability and/or groundwater flow, allowing for high net extraction of fluids and the displacement of large amounts of groundwater.
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Composting
The process of composting involves the controlled conversion of degradable organic products and wastes into stable products with the aid of microorganisms. Composting is a biological decomposition process that requires oxygen and is carried out by microorganisms. These microorganisms feed on the materials added to the compost pile, using carbon and nitrogen to grow and reproduce, water to digest materials, and oxygen to breathe.
The end product of composting is compost, a biologically stable soil amendment that can be used to build soil health and provide nutrients to plants. Compost contains the three primary nutrients needed by garden crops: nitrogen, phosphorus, and potassium, as well as traces of other essential elements like calcium, magnesium, iron, and zinc. By applying compost to the soil, farmers can increase soil's water retention capacity, productivity, and resiliency, leading to higher yields.
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Preventing pollution
Soil contamination is a pressing environmental issue that affects human health, biodiversity, and food security. It is caused by the introduction of harmful substances, such as chemicals, metals, or pathogens, into the soil through human activities or natural processes. Here are some detailed and instructive guidelines focused on preventing soil pollution:
Identify Pollutant Sources:
The first step is to identify the potential sources of pollutants. These may include industrial activities, agricultural practices, waste disposal sites, mining, fuel spills, or natural disasters. Site inspections, historical records, environmental audits, and risk assessments can help determine the type, amount, and distribution of pollutants, enabling the development of targeted prevention strategies.
Implement Best Practices:
Adopting best practices can reduce or eliminate the release of pollutants into the soil. This includes using cleaner production techniques, integrated pest management, organic farming methods, and proper waste management. Preventing leaks and spills, using protective barriers, and educating stakeholders on safe handling and disposal of hazardous substances are also crucial aspects of pollution prevention.
Proper Waste Disposal:
Improper waste disposal is a significant contributor to soil pollution. It is essential to ensure the proper treatment of waste prior to its release into the environment. This includes categorizing waste according to contamination levels and managing heavily contaminated waste strictly to avoid serious consequences. Neutralizing highly acidic or alkaline waste before disposal is an important step in preventing soil contamination.
Minimize Chemical Usage:
Chemical pesticides and fertilizers can have long-term detrimental effects on soil quality. It is advisable to minimize the use of these chemicals and opt for organic alternatives. While they may offer immediate benefits, the accumulation of contaminants over time can impact soil health and productivity. Consulting with experts before using new products can help address doubts about their safety and potential environmental impact.
Regular Soil Monitoring:
Regular and systematic monitoring of soil quality is essential for prevention. Utilizing tools and indicators to measure physical, chemical, and biological soil properties, as well as the presence and concentration of pollutants, allows for early detection of anomalies. Employing sensors, drones, or satellites can enhance data collection and analysis, enabling proactive corrective actions to protect soil health.
By following these preventive measures, we can effectively reduce the risk of soil pollution, safeguard our natural resources, and ensure a healthier environment for future generations.
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Frequently asked questions
Soil remediation is the practice of cleaning up contaminated soil. Some methods of soil remediation include:
- Bioremediation: Using biological processes and microorganisms such as bacteria and fungi to degrade, transform, or remove contaminants.
- Chemical oxidation: Injecting reactive chemical oxidants to destroy contaminants.
- Soil washing: Using water to separate or remove contaminants.
- Thermal desorption: Using heat to drive off volatile contaminants.
- Air injection: Introducing air into the polluted zone to volatilize contaminants.
Soil pollution is mostly caused by chemical substances and hazardous substances produced by human activity. Some common causes include:
- Poor waste disposal methods
- Oil spillages
- Industrial activities
- Pesticides and fertilizers
- Agricultural chemicals
It is recommended to consult with a soil remediation expert to develop a personalized plan for your property. Here are some general tips:
- Minimize the use of chemical pesticides and fertilizers.
- Focus on pollution prevention rather than remediation by properly managing waste disposal and avoiding the use of hazardous substances.
- Use polymers to improve water and nutrient retention in the soil, enhancing its health and cleanliness.
